(1) Field of the Invention
This invention relates to a pixel device of a transflective-type liquid crystal panel, and more particularly to a pixel device that replaces quarter-wave plates and half-wave plates functionally with a liquid crystal film.
(2) Description of Related Art
Recently, liquid crystal displays (LCD) become more popular than ever as a display component of personal digital assistants (PDA), notebooks (NB), digital cameras (DC), digital videos (DV), mobile phones, etc. Due to lack of self-illumination, a cold cathode fluorescent lamp (CCFL) is inserted in the LCD as a backlight source. In addition, several optical films are sandwiched layer-wise between the backlight and the panel to form a light path or quasi-lens.
Ordinarily, less than 10% the illumination of the backlight is able to reach human eyes in front of the panel to display image, and the rest of illumination is actually blocked by the optical films and the liquid crystal layer of the panel. Therefore, a reflective-type LCD is developed for achieving a better power consumption than conventional LCD. The reflective-type LCD uses ambient illumination as the light source, and so the CCFL and the optical films are no longer needed in this type of display panel. As a result, the power consumption of the transflective-type display can be lowered down and also the size can be slimmer. Yet, when the ambience is dark, the performance of the reflective-type LCD would be poor.
Thereby, the transflective-type LCD is introduced to integrate advantages of the transmission-type and reflective-type LCD. The usage of the ambient light or backlight can be optioned according to the environmental brightness. When the ambient light is sufficient, this LCD can function as a reflective-type one and so the power consumption can be saved. On the other hand, when the ambience is dark, this LCD can function as a transmission-type one and so the required illumination is provided by the backlight.
Referring to FIG. 1, a pixel device of a traditional transflective-type LCD comprises an upper panel 100, a lower panel 300, and an interposed liquid crystal layer 200. The upper panel 100 is composed mainly of a glass substrate 108. A quarter-wave plate 106, a half-wave plate 104, and a first polarizer 102 are formed layer-by-layer over an upper surface of the glass substrate 108. A color filter layer 110 and a common electrode layer 112 are attached, also layer-by-layer, to a lower surface of the glass substrate 108. The lower panel 300 is composed mainly of a glass substrate 308. A quarter-wave plate 306, a half-wave plate 304, and a second polarizer 302 are attached layer-wise to a lower surface of the glass substrate 308. A pixel electrode layer 312 and a reflector 314 are formed layer-wise in a serial over an upper surface of the glass substrate 308. The reflector 314 as shown includes an organic layer 3142 plated with a reflective film 3144. The reflective film 3144 is composed of a conductive material and connects to the pixel electrode layer 312. Thereby, the upper surface of the glass substrate 308 is divided into a transmission region T and a reflector 314 denoted as a reflective region R. Upon such an arrangement, the liquid crystal layer 200 can be driven to display images by an electric field formed between the common electrode layer 112 and the pixel electrode layer 312.
It is noticed that the ambient light passes through the liquid crystal layer 200 twice in the reflective region R, whereas the backlight passes through the liquid crystal layer 200 merely once in the transmission region T. As a result, contributions of the liquid crystal layer 200 toward the ambient light or the backlight are different. As shown in FIG. 1, a traditional method to compensate the difference is utilized to modulate the thickness of the liquid crystal layer 200 in the reflective region R by changing the thickness of the organic layer 3142.
The polarizers 102 and 302 are set at a particular polarizing direction to shield a portion of the ambient light and the backlight so as to have linear polarized lights entering the pixel device. The quarter-wave plates 106 and 306 are used to transform the linear polarized light into circular polarized one, so that the liquid crystal layer 200 is able to adjust the polarization of the ambient light and the backlight. It is noted that the quarter-wave plates 106 and 306 are designed within a certain frequency range. Thus, to have those foregoing plates operated at a frequency beyond the design frequency range will definitely cause a significant bias. The half-wave plates 104 and 304 are used mainly for spreading the frequency range of the quarter-wave plates 106 and 306 so as to make sure that the linear polarized light can be transformed into an ideal circular polarized light throughout the whole visible light frequency range.
As mentioned in the above paragraph, the polarizers 102 and 302, the quarter-wave plates 106 and 306, and the half-wave plates 104 and 304 are necessary in order to have the traditional LCD properly function. However, the cost of forming such optical modulation structures is obviously high, and the manufacturing process is too complicated to have a satisfied yield.